I just saw Avatar in IMAX 3D. The 3D process is great. Even though the tickets are incredibly expensive, see it this way if you at all can. It's really a beautiful treat for the eyes.
Don't worry about the story. It's Dances With Wolves meets Dune. It will impress a lot of non-sf people with the imagination of sf. I'm sure it will earn James Cameron back the phenomenal amount of money that was spent on it. Most important, I hope the technology will trickle down into other film-making so that more imaginative stories can eventually be filmed.
I had fun. Go for the visual experience, and don't expect to think too hard.